[Rd] mcmapply Core Usage

[Simon Urbanek]

Dario,

yes, that is a bug, now fixed.

Cheers,
Simon


On May 29, 2014, at 2:00 AM, Dario Strbenac <dstr7320 at uni.sydney.edu.au> wrote:

> Hello,
> 
> I have a minimal example that shows a problem I'm having with parallel processing.
> 
> library(parallel)
> mcmapply(function(x, y)
> {
>  print("Running")
>  Sys.sleep(10)
> }, as.list(1:10), as.list(10:1), mc.cores = 16, SIMPLIFY = FALSE)
> 
> I see "Running" printed once every ten seconds. I read the documentation for mcmapply, but I don't understand why it wouldn't print all ten output statements almost at once, then wait for about ten seconds, then return to the prompt. Is it documented in another location ?
> 
> My problem is that I have a section of code that takes a long time, which I have replaced with Sys.sleep in the above example, but when I look at the output of top, I only see 1 CPU being used. The computer has 16 processors.
> 
>> sessionInfo()
> R version 3.1.0 (2014-04-10)
> Platform: x86_64-pc-linux-gnu (64-bit)
> 
> locale:
> [1] LC_CTYPE=en_AU.UTF-8       LC_NUMERIC=C              
> [3] LC_TIME=en_AU.UTF-8        LC_COLLATE=en_AU.UTF-8    
> [5] LC_MONETARY=en_AU.UTF-8    LC_MESSAGES=en_AU.UTF-8   
> [7] LC_PAPER=en_AU.UTF-8       LC_NAME=C                 
> [9] LC_ADDRESS=C               LC_TELEPHONE=C            
> [11] LC_MEASUREMENT=en_AU.UTF-8 LC_IDENTIFICATION=C       
> 
> attached base packages:
> [1] parallel  stats     graphics  grDevices utils     datasets  methods  
> [8] base     
> 
> loaded via a namespace (and not attached):
> [1] tools_3.1.0
> 
> --------------------------------------
> Dario Strbenac
> PhD Student
> University of Sydney
> Camperdown NSW 2050
> Australia
> 
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